Glucose strip sensor and glucose measurement method using the glucose strip sensor

ABSTRACT

Disclosed is a disposable glucose strip sensor configured to rapidly and conveniently measure the concentration of glucose in blood and a glucose measurement method using the glucose strip sensor. In the glucose strip sensor, at least one checking electrodes are additionally provided at an electrode section including an operating electrode and a counter electrode. The checking electrode serves to check whether or not it is electrically connected with the counter electrode, upon measuring the concentration of glucose in a blood sample introduced in the sensor. Where two checking electrodes are provided, it may be checked whether or not an electrical connection is established between those checking electrodes. Based on the result of the checking, it is possible to determine whether or not a sufficient amount of blood sample is filled in the sensor. Accordingly, the measurement of glucose concentration can be accurately achieved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a disposable glucose strip sensorconfigured to rapidly and conveniently measure the concentration ofglucose in blood and a glucose measurement method using the glucosestrip sensor.

2. Description of the Related Art

The measurement of the concentration of glucose in blood is of greatimportance not only to diabetic patients who must control their sugarintake, but also for the early detection and diagnosis of diabetes. Tothis end, methods for simply and conveniently measuring theconcentration of glucose in blood have been proposed.

Known glucose measurement methods are based on oxidation of glucose byglucose-oxidase and peroxidase. They also use orthotolidine or abenzidine-based mixture as an indicator reagent, that is, a chromogen.In accordance with these methods, a color transition of the indicatorreagent resulting from the oxidation of glucose is observed to measurethe concentration of glucose in blood.

For example, such techniques are disclosed in U.S. Pat. No. 3,061,523and Japanese Patent Publication No. Sho. 50-39558. In these references,a glucose-measuring test piece is disclosed. In order to prepare thistest piece, a solution is prepared which has a composition including:glucose oxidase and peroxidase as enzymes; a citric acid buffer tomaintain a pH of 6.0; gelatin, alginic acid, polyvinylpyrrolidone, andpolyvinyl alcohol as stabilizers; and orthotolidine, benzidine,3-aminopropylcarbarsone, and 2,7-diaminofluorene as a chromogen. Thesolution is impregnated into a cellulose paper which has a desiredthickness and size to be used as a carrier, and then dried. Thus, thetest piece is obtained. Also, Korean Patent Laid-open Publication No.85-1297 discloses a method for manufacturing a glucose-measuring testpiece, to which the basic principle of an enzymatic measurement methodusing glucose oxidase and peroxidase is applied. Where the concentrationof glucose in blood is measured using the above mentionedglucose-measuring test pieces, it is difficult to accurately measure aglucose concentration because the measurement is based on a colortransition exhibited on the test piece.

In order to solve the above mentioned problem, various techniques havebeen proposed which measure glucose concentration using anelectrochemical method. Such an electrochemical method makes it possibleto measure the concentration of glucose in blood with an increasedaccuracy while reducing measurement time and achieving convenience inmeasurement. By virtue of such advantages, the use of theelectrochemical glucose measurement method has been greatly increased.

Now, the operating principle of a glucose-measuring sensor based on anelectrochemical method will be described. When a blood sample is appliedto a reaction layer of the glucose-measuring sensor, glucose containedin the blood sample is oxidized by a glucose-oxidizing enzyme containedin the reaction layer. At this time, the glucose-oxidizing enzyme isreduced. The reduced glucose-oxidizing enzyme is then oxidized by anelectron acceptor, whereby the electron acceptor is reduced. The reducedelectron acceptor donates electrons at the surface of an electrode towhich a desired voltage is applied. As a result, the electron acceptoris electrochemically reoxidized. The concentration of glucose in theblood sample is proportional to the amount of current generated duringthe process in which the electron acceptor is oxidized. Accordingly, theconcentration of glucose can be measured by measuring the amount ofcurrent.

An example of the above mentioned glucose-measuring sensor is disclosedin Japanese Patent Laid-open Publication No. 61-294351. This sensor isillustrated in FIG. 1. As shown in FIG. 1, operating and counterelectrodes, which are made of carbon or the like, are formed on asubstrate 111 in a screen printing fashion. An insulator 115 is alsoformed on the substrate 111 while allowing the electrodes to bepartially exposed. A porous reaction layer 117, which contains areactive material such as a glucose-oxidizing enzyme and an electronacceptor, is arranged on the insulator 115. In order to firmly hold theporous reaction layer 117, a holding frame 116 and a cover 118 arearranged on the insulator 115. In FIG. 1, reference numerals 112, 113,and 114 denote the operating and counter electrodes, and referencenumerals 112′, 113′, and 114′ denote the exposed portions of theoperating and counter electrodes. These electrodes and electrodeportions form an electrode system. When a blood sample is dropped ontothe porous reaction layer 117, the glucose-measuring sensor having theabove mentioned structure can measure the concentration of glucose inthe blood sample.

In this glucose-measuring sensor, however, the amount of blood absorbedin the reaction layer 117 varies depending on the amount of the bloodsample dropped onto the reaction layer 117. As a result, measurementerrors may be caused by a variation in the amount of blood absorbed inthe reaction layer 117.

In order to solve this problem, a biosensor has been proposed. Anexample of such a biosensor is disclosed in U.S. Pat. No. 5,120,420 andillustrated in FIG. 2. As shown in FIG. 2, this biosensor includes anon-conductive substrate 211 made of polyethylene terephthalate. Silveris screen-printed on the non-conductive substrate 211 to form leads 212and 213. Conductive carbon paste containing a resin binder is printed onthe leads 212 and 213, thereby forming an operating electrode 214 and acounter electrode 215. An insulator 216 is then printed to allow theelectrodes 214 and 215 to be partially exposed. A 0.5% aqueous solutionof carboxymethyl cellulose (CMC) is spread onto the electrodes 214 and215, and dried to form a CMC layer. A solution of glucose oxidase (GOD)as the enzyme in a phosphate buffer solution is spread on the CMC layer,and dried to form a main reaction layer comprised of a CMC-GOD layer.Next, a resin plate 217 and a cover 219 are attached to the resultingstructure while defining a space 218. In FIG. 2, the reference numeral220 denotes a sample introducing port, and the reference numeral 221denotes a discharge port.

In the biosensor having the above mentioned structure, when a samplesolution comes into contact with the sample introducing port 220, it isintroduced into the space 218 by virtue of capillary phenomenon, so thatit fills the space 218. Simultaneously, air existing in the space 218 isvented from the space 218 through the discharge port 221 formed oppositeto the sample introducing port 220 or at the cover 219.

Where the discharge port 221 is arranged at the upper surface of thebiosensor, measurement errors may occur when the user unintentionallytouches the discharge port 221. For this reason, there is inconveniencein handling the biosensor. Furthermore, the user can check whether ornot a sufficient amount of sample solution is introduced in thebiosensor, only with the naked eye. So, the measurement may be carriedout even when an insufficient amount of sample solution is filled in thebiosensor. In this case, however, the detected glucose level mayerroneously be lower than the actual glucose concentration.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above mentionedproblems involved with the conventional glucose-measuring sensors, andan object of the invention is to provide a glucose strip sensorincluding a sample introducing port arranged at a front surface of thesensor, and discharge ports respectively arranged at opposite sidesurfaces of the sensor, thereby being capable of achieving conveniencein handling the sensor, while additionally including a checkingelectrode adapted, alone or along with a counter electrode, to determinewhether or not a sufficient amount of blood sample is introduced in thesensor, thereby being capable of achieving an accurate glucosemeasurement, and to provide a glucose measurement method using theglucose strip sensor.

In accordance with one aspect, the present invention provides a glucosestrip sensor comprising a non-conductive substrate, a lead sectionformed on the substrate, the lead section including leads and leadterminals, an electrode section formed on the lead section and providedat an upper surface thereof with a reaction layer, the electrode sectionincluding an operating electrode, a counter electrode, and a checkingelectrode, a resin plate adapted to define, over the electrode section,a space for receiving a blood sample, a cover formed on the resin plate,a sample introducing port adapted to introduce the blood sample into thespace, and discharge ports adapted to vent air from the space, wherein:

the electrode section further includes at least one checking electrodeadapted to check whether or not the blood sample is completelyintroduced in the space; and

the lead section further includes a lead and a lead terminal for thechecking electrode.

The sample introducing port may be arranged at a front surface of thesensor, and the discharge ports are arranged at opposite side surfacesof the sensor, respectively.

In accordance with another aspect, the present invention provides aglucose measurement method comprising the steps of checking whether ornot an electrical connection is established between the counterelectrode and the checking electrode included in the glucose stripsensor or between the checking electrode and another checking electrode,thereby determining whether or not a blood sample is introduced in thespace in a sufficient amount; and if it is determined the blood sampleis introduced in the space in a sufficient amount, then measuring aglucose concentration of the blood sample in accordance with awell-known method.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the drawings, in which:

FIG. 1 is an exploded perspective view illustrating a conventionalsample-dropped glucose-measuring test piece;

FIG. 2 is an exploded perspective view illustrating a conventionalglucose-measuring biosensor utilizing capillary phenomenon;

FIG. 3 is an exploded perspective view illustrating a glucose stripsensor according to an embodiment of the present invention;

FIG. 4 is a sectional view of the glucose strip sensor illustrated inFIG. 3;

FIG. 5 is an assembled perspective view of the glucose strip sensorillustrated in FIG. 3;

FIG. 6 is a perspective view illustrating an electrode arrangement inthe glucose strip sensor according to the present invention;

FIG. 7 is a perspective view illustrating another electrode arrangementin the glucose strip sensor according to the present invention; and

FIG. 8 is a graph depicting the correlation of a signal generated by theglucose strip sensor according to the present invention with respect toglucose concentration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 is an exploded perspective view illustrating a glucose stripsensor according to an embodiment of the present invention. FIG. 4 is asectional view of the glucose strip sensor illustrated in FIG. 3. FIG. 5is an assembled perspective view of the glucose strip sensor illustratedin FIG. 3.

As shown in FIGS. 3 to 5, the glucose strip sensor includes anon-conductive substrate 10, a lead section 20 formed on the substrate10 by a silver ink or an ink mixture of silver and silver chloride, andan electrode section 30 formed on the lead section 20. The lead section20 includes leads 21 and lead terminals 22, whereas the electrodesection 30 includes an operating electrode 31, a counter electrode 32,and a checking electrode 33. The glucose strip sensor also includes aninsulating layer 40 coated on the lead and electrode sections 20 and 30while allowing the lead and electrode sections 20 and 30 to be partiallyexposed, a reaction layer 50 formed on the exposed portion of theelectrode section 30, a resin plate 60 formed on the structure obtainedafter the formation of the reaction layer 50, and a cover 70 formed onthe resin plate 60. The resin plate 60 defines a space 63, a sampleintroducing port 61, and discharge ports 62. The sample introducing port61 is arranged at the front surface of the glucose strip sensor, whereasthe discharge ports 62 are arranged at opposite side surfaces of theglucose strip sensor, respectively.

The glucose strip sensor of the present invention is characterized inthat it includes, in addition to the operating electrode 31 and counterelectrode 32, the checking electrode 33 for checking whether or not asample is completely introduced in the sensor. The glucose strip sensorof the present invention is also characterized in that the sampleintroducing port 61 is arranged at the front surface of the glucosestrip sensor, whereas the discharge ports 62 are arranged at oppositeside surfaces of the glucose strip sensor, respectively.

Now, the fabrication of the glucose strip sensor having the abovedescribed structure will be described in detail.

First, the substrate 10 is prepared. For the substrate 10, a polymersubstrate may be used which is made of a non-conductive material such aspolyethylene terephthalate, polyvinyl chloride resin, or polycarbonateresin. The substrate 10 is preferably made of polyethyleneterephthalate.

The formation of the lead section 20 on the substrate 10 is thenperformed. As mentioned above, the lead section 20 includes the leads 21and lead terminals 22. The lead section 20 may be formed using awell-known screen printing method. In accordance with the presentinvention, the lead section 20 is formed by screen-printing a silver inkor an ink mixture of silver and silver chloride on the substrate 10.

After formation of the lead section 20, the electrode section 30 isformed on the lead section 20. In accordance with the present invention,the electrode section 30 includes the checking electrode 33 in additionto the operating electrode 31 and counter electrode 32. Although onechecking electrode 33 is illustrated, the electrode section 30 mayinclude two or more checking electrodes. Where the checking electrode 33is arranged as shown in FIG. 6, it is checked whether or not thechecking electrode 33 is electrically connected with the counterelectrode 32. Based on the result of the checking, it is possible todetermine whether or not the blood sample is sufficiently filled in thesensor. Accordingly, the glucose concentration in the blood sample canbe accurately measured.

Under the condition in which the checking electrode 33 a determines thata sufficient amount of blood sample is introduced in the sensor, thechecking electrode 33 can perform the same function as the counterelectrode 32 because the checking electrode 33 is electrically connectedwith the counter electrode 32. In this case, an increased counterelectrode area is obtained. By virtue of such an increased counterelectrode area, it is possible to obtain a glucose measuring signal withan increased sensitivity when the amount of current flowing between theoperating electrode and the counter electrode is measured. The operatingelectrode 31 and counter electrode 32, which form the electrode section30, may be formed using a well-known method. The formation of thechecking electrode 33 may also be achieved in the same manner as theformation of the counter electrode 32. As mentioned above, the electrodesection 30 is preferably formed in accordance with a screen printingmethod using a conductive carbon ink.

On the upper surface of the resulting structure obtained after formationof the electrode section 30, an insulating material is screen-printed toform the insulating layer 40 for insulating the lead section 20 whilepartially exposing the electrode section 30. For the insulatingmaterial, a non-conductive screen printing ink or an insulating ink maybe used. In accordance with the present invention, the insulating screenprinting ink is preferably used. Thereafter, the formation of thereaction layer 50 is carried out in such a fashion that the reactionlayer 50 covers the exposed portion of the electrode section 30. Thereaction layer 50 is made of a material including hydrogel and glucoseoxidase (GOD) as major components thereof. In detail, the formation ofthe reaction layer 50 is achieved by preparing a solution obtained byrespectively mixing hydrogel, GOD and a stabilizer in a liquid buffer atdesired rates, dispensing the solution onto the surface of the electrodesection 30, and then drying the dispensed solution in an incubator.

On the resulting structure obtained after formation of the reactionlayer 50 including hydrogel and GOD as major components thereof, a resinplate 60 is arranged to define a space 63. Also, the resin plate 60defines the sample introducing port 61 at the front surface of thesensor and the discharge ports 62 at respective side surfaces of thesensor. Since the sample introducing port 61 and discharge ports 62 areformed at the front and side surfaces of the sensor, respectively, it ispossible to conveniently handle the sensor, as compared to theconventional sensor including a discharge port formed at the uppersurface of the sensor.

The cover 70 is finally arranged on the resin plate 60 using awell-known method. Thus, the fabrication of the glucose strip sensoraccording to the present invention is completed.

Since the glucose strip sensor having the above mentioned structureincludes the checking sensor 33, it is possible to check whether or notthe checking sensor 33 is electrically connected with the counterelectrode 32, thereby determining whether or not the sensor is filledwith a sufficient amount of blood sample. Accordingly, there is anadvantage in that the measured glucose concentration has an increasedaccuracy. In addition, where the amount of current flowing between thecounter electrode 32 and the checking electrode 33 is measured under thecondition in which those electrodes are electrically connected usingconduction means, there is an advantage in that a glucose measuringsignal with an increased sensitivity can be obtained. Since the sampleintroducing port 61 and discharge ports 62 are formed at the front andside surfaces of the sensor, respectively, it is also possible toconveniently handle the sensor.

In the case of FIG. 3, the arrangement of the operating electrode 31,counter electrode 32, and checking electrode 33 is made in such afashion that the counter electrode 32 and checking electrode 33 arearranged at front and rear sides of the operating electrode 31,respectively. However, other arrangements may be implemented.

For example, the counter electrode 32 may be arranged near the sampleintroducing port 61, and the checking electrode 33 may be arranged nearone of the discharge ports 62, as shown in FIG. 6. In this case, thechecking electrode 33 is electrically connected with the counterelectrode 32 under the condition in which the space 63 of the sensor iscompletely filled with a blood sample. Accordingly, it is possible toaccurately check whether or not the space of the sensor is completelyfilled with a blood sample even when the space has an increased volume.

It is also possible to arrange the checking electrode 33 near the sampleintroducing port 61 while arranging the counter electrode 32 in rear ofthe operating electrode 31, as shown in FIG. 7.

Using the checking electrode having the arrangement illustrated in FIG.6 or 7, it is possible to accurately determine whether or not asufficient amount of blood sample is introduced in the sensor.Accordingly, measurement errors can be reduced.

The operation of the glucose strip sensor having the above describedstructure according to the present invention will now be described indetail. When a blood sample comes into contact with the sampleintroducing port 61 of the sensor, it is introduced into the space 63 ofthe sensor by virtue of capillary phenomenon, so that it fills the space63. Simultaneously, air existing in the space 63 is vented from thespace 63 through the discharge ports 62 respectively formed at oppositeside surfaces of the sensor. Thereafter, it is checked, prior to adesired measurement of glucose concentration, whether or not asufficient amount of blood sample is introduced in the space 63. Thatis, it is checked whether or not an electrical connection is establishedbetween the counter electrode 32 and the checking electrode 33.

The blood sample filled in the space 63 of the sensor is impregnatedinto the reaction layer 50. The glucose of the impregnated blood sampleenzymatically reacts with the GOD contained in the reaction layer 50, sothat it is oxidized. Simultaneously, the GOD is reduced. The reduced GODis then oxidized as it reacts with the electron acceptor contained inthe reaction layer 50, whereas the oxidized GOD reacts with the glucosenot yet oxidized. The reduced electron acceptor migrates to the surfaceof the operating electrode 31, to which voltage of about 0.6 V isapplied, and donates electrons at that surface. Simultaneously, theelectron acceptor is reoxidized so that it takes part again in the abovereaction. The current generated during the oxidation of the electronacceptor is proportional to the concentration of glucose in the bloodsample. Accordingly, the glucose concentration in the blood sample canbe quantitatively derived by measuring the amount of current flowingbetween the operating electrode 31 and the counter electrode 32.

An experiment was made in order to identify correlations establishedbetween the glucose concentration measured by the glucose strip sensoraccording to the present invention and the glucose concentrationmeasured by an automatic glucose analyzer. The experiment was carriedout as follows.

First, a blood sample was prepared by dissolving a desired amount ofglucose in a buffer solution. Thereafter, the concentration of glucosein the blood sample was measured using an automatic glucose analyzer,which is the Model YSI 2300 STAT PLUS manufactured by YSI Inc. Thesignal intensity corresponding to the measured glucose concentration wasthen measured by the glucose strip sensor according to the presentinvention. The correlation between the measured glucose concentrationand the measured signal intensity is depicted in FIG. 8. The measurementwas repeated 6 times for each glucose concentration.

Referring to FIG. 8, it can be seen that the correlation between themeasured glucose concentration and the measured signal intensity is wellestablished in a clinically important glucose concentration range, thatis, a glucose concentration range of 50 to 600 mg/dL.

As apparent from the above description, the present invention provides aglucose strip sensor in which a checking electrode is additionallyprovided at an electrode section including an operating electrode and acounter electrode. The checking electrode serves to check whether or notit is electrically connected with the counter electrode, upon measuringthe concentration of glucose in a blood sample introduced in the sensor.Based on the result of the checking, it is possible to determine whetheror not a sufficient amount of blood sample is filled in the sensor.Accordingly, the measurement of glucose concentration can be accuratelyachieved. Moreover, where the amount of current flowing between thecounter electrode and the checking electrode is measured under thecondition in which those electrodes are electrically connected usingconduction means, there is an advantage in that a glucose measuringsignal with an increased sensitivity can be obtained.

In accordance with the present invention, the glucose strip sensor alsoincludes a sample introducing port arranged at the front surface of thesensor, and discharge ports arranged at respective side surfaces of thesensor. Accordingly, it is also possible to conveniently handle thesensor.

Although the preferred embodiments of the invention have been disclosedfor illustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the invention as disclosed in theaccompanying claims.

1. A glucose strip sensor comprising: a non-conductive substrate; anelectrode section formed on the substrate, the electrode sectionincluding an operating electrode and a counter electrode respectivelyelectrically connected to lead terminals by leads; a reaction layerformed over the electrode section and being adapted to react with ablood sample; a resin plate adapted to define, over the electrodesection, a sample receiving space for receiving the blood sample; acover arranged on the resin plate; a sample introducing port arranged ona front end portion of the resin plate, the sample introducing portbeing adapted to introduce the blood sample into the sample receivingspace by virtue of capillary phenomenon; and discharge ports arranged onopposite sides of the glucose strip sensor and being defined by theresin plate, the discharge ports being adapted to vent air from thesample receiving space, wherein the electrode section further comprisesat least one checking electrode arranged near one of the dischargeports, the at least one checking electrode being adapted to checkwhether or not the blood sample is completely introduced in the samplereceiving space.
 2. The sensor of claim 1, wherein the at least onechecking electrode is electrically connected with the counter electrodeunder the condition in which the sample receiving space is completelyfilled with the blood sample, whereby the checking electrode functionsto increase a area of the counter electrode, whereby a glucose measuringsignal with an increased sensitivity is obtained.
 3. The sensor of claim1, wherein the glucose strip sensor comprises a lower surface defined bythe substrate, a upper surface defined by the cover, a front edge andside edges defined by the cover, the substrate, and the resin plate. 4.The sensor of claim 1, wherein the sample introducing port is arrangedon a front side edge of the glucose strip sensor.
 5. The sensor of claim1, wherein the discharge ports are arranged on opposite side edges ofthe glucose strip sensor.
 6. The sensor of claim 1, wherein the sampleintroducing port is arranged on a front side edge of the glucose stripsensor and is defined by the cover, the resin plate, and the substrate.7. The sensor of claim 1, wherein the discharge ports are arranged onopposite side edges of the glucose strip sensor and is defined by thecover, the resin plate, and the substrate.
 8. The sensor of claim 1,wherein the non-conductive substrate comprises a non-conductive polymermaterial comprising at least one of polyvinyl chloride resin andpolycarbonate resin.
 9. The sensor of claim 1, wherein the leads areformed by screen printing.
 10. The sensor of claim 1, wherein thereaction layer comprises at least hydrogel and glucose oxidase.
 11. Aglucose measurement method comprising: introducing a blood sample intothe glucose strip sensor comprising a non-conductive substrate, anelectrode section formed on the substrate, the electrode sectionincluding an operating electrode and a counter electrode respectivelyelectrically connected to lead terminals by leads, a reaction layerformed over the electrode section and being adapted to react with ablood sample, a resin plate adapted to define, over the electrodesection, a sample receiving space for receiving the blood sample, acover arranged on the resin plate, a sample introducing port arranged ona front end portion of the resin plate, the sample introducing portbeing adapted to introduce the blood sample into the sample receivingspace by virtue of capillary phenomenon, and discharge ports arranged onopposite sides of the glucose strip sensor and being defined by theresin plate, the discharge ports being adapted to vent air from thesample receiving space, wherein the electrode section further comprisesat least one checking electrode arranged near one of the dischargeports, the at least one checking electrode being adapted to checkwhether or not the blood sample is completely introduced in the samplereceiving space; checking whether or not an electrical connection isestablished between the counter electrode and the checking electrode inorder to determine whether or not the blood sample is introduced in thesample receiving space in a sufficient amount; and if it is determinedthe blood sample is introduced in the sample receiving space in asufficient amount, having the counter electrode also function as acounter electrode thereby increasing the counter electrode area, wherebya glucose measuring signal with an increased sensitivity is obtained;and measuring a glucose concentration of the blood sampleelectrochemically.